Signature mismatch: Modules do not match:

[Secomxslw]

• ocamlfind ocamlc -c -g -package gsl -pp ocaml+twt -o PhyloLik.cmo PhyloLik.ml
  File "PhyloLik.ml", line 7, characters 25-28:
  7 | pe leaf = [Certain of int | Distribution of float array | Marginalize] ^^^ Error: Signature mismatch: Modules do not match: sig type t = int val compare : ('a -> 'a -> int) -> 'a list -> 'a list -> int end is not included in Set.OrderedType Values do not match: val compare : ('a -> 'a -> int) -> 'a list -> 'a list -> int is not included in val compare : t -> t -> int File "set.mli", line 55, characters 4-31: Expected declaration File "PhyloLik.ml", line 6, characters 5-12: Actual declaration Command exited with code 2. Compilation unsuccessful after building 51 targets (49 cached) in 00:00:01. make[2]: *** [lib] Error 10 make[2]: Leaving directory /home/ykf/CSF/PhyloCSF/lib/CamlPaml'
  make[1]: *** [reinstall] Error 2
  make[1]: Leaving directory `/home/ykf/CSF/PhyloCSF/lib/CamlPaml'
  make: *** [CamlPaml] Error 2

This is an error message. What does it mean? How can I resolve it? Thank you, everyone.